Helicobacter pylori is a bacterium known to cause peptic ulcer disease and stomach cancer. Although H. pylori commonly infects humans, its mode of transmission remains unknown. Without knowing how infection is transmitted, it is difficult to prevent infection from occurring. In this study, we are seeking to determine how humans-the primary host for H. pylori-shed the organism into the environment. Because H. pylori lives in the stomach, we presume it is excreted through the mouth or in stools. In this study, we intensively look for H. pylori in saliva, vomit, air during vomiting and in stools (both diarrheal and normal) from healthy young volunteers. To do this, we admit patients to the General Clinical Research Center and induce short periods of vomiting and diarrhea using common over-the-counter medications. We also evaluate whether the ability of the stomach to secrete acid affects whether H. pylori is excreted in stools. It is our hope that by understanding H. pylori transmission, we will better be able to prevent infection and its associated diseases in the future.